This open study will have two parallel groups based on the vaccination received in the primary study: AC primed Group: primed with Tritanrix™-HepB/Hib-MenAC vaccine and AC unprimed Group (control): primed with Tritanrix™-HepB/Hiberix™ vaccine. All subjects will receive a booster dose of Tritanrix™-HepB/Hiberix™ vaccine at 15 to 18 months of age with GSK Biological's OPV vaccine given concomitantly and a dose of Mencevax™ ACW vaccine at 24 to 30 months of age. Blood sampling will be done prior to (pre) and one month after (post) the Mencevax™ ACW vaccine administration for immunogenicity analyses. The study will last minimum 7 to maximum 16 months per subject.